Ma'anar ƙamus na kalmar "myasthenia" yanayi ne na likita wanda ke da rauni da saurin gajiyar tsokoki na son rai. Kalmar "myasthenia" ta fito ne daga kalmomin Helenanci "myo" ma'ana tsoka da "asthenia" ma'ana rauni. Myasthenia yawanci yana haifar da matsala tare da watsa abubuwan motsa jiki zuwa tsokoki, kuma yana iya shafar tsokoki daban-daban a cikin jiki, ciki har da waɗanda ake amfani da su don numfashi, magana, da haɗiye. Akwai nau'o'in myasthenia da yawa, ciki har da myasthenia gravis, wanda shine rashin lafiyar jiki wanda ke shafar mahadar neuromuscular.